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Materials science investigates the structure and properties of different materials. One of these materials is the crystal. Crystals are solid materials with building blocks (atoms, ions, or molecules) that are arranged in a highly organized manner. Salt, quartz, and diamonds are examples of crystals. In ordinary crystals, these building blocks are organized in a repeating pattern in all directions. In contrast, in special crystals called quasi-crystals, the building blocks are organized in a non-repeating manner. The discovery of quasi-crystals created a revolution in the science of crystallography and changed our most basic definition of a crystal. Since their discovery, many hundreds of quasi-crystals have been found. Some of these quasi-crystals have unique physical properties and are useful for a variety of different applications.

Ductile iron bars (DIBs) with a diameter of 145 mm, used for plunger pump production, were made by the horizontal continuous casting (HCC). The microstructure of the samples cut at three locations with different distances away from the surface (~20 mm from the surface, half of the radius and the center of the HCCDIBs) were investigated. The mechanical properties were measured by tensile and torsion tests. Results show that after the spheroidization of graphite, the iron matrix incorporates the nodules of Format I, Size 8 close to the surface, Format I, Size 7 at the half of the radius from the surface, and Format II, Size 6 in the centre of the bar, according to the ASTM A247 standard. The content of pearlite in the matrix changes from 55% (~20 mm from the surface) to 70% (half of the radius) and 80% (the center of the HCCDIBs). The strengths in tension are 552, 607 and 486 MPa with the elongations of 12.5%, 10.5% and 5.8% in samples cut at these three locations from the surface to the centre, respectively. The strength in torsion is equal to 558, 551 and 471 MPa at corresponding torsion angles of 418°, 384° and 144° respectively to the same distance from the bar surface. Fracture in tension is manifested via crack propagation through the interface between graphite nodules and matrix (Mode I), while in torsion the fracture is caused by the shear of graphite nodules (Mode II). It is shown that the transition between two fracture modes is also dependent on the size of graphite nodule. Typically, fracture Mode I was observed for nodules of smaller diameter (less than 22.7 μm) and fracture Mode II was seen for nodules of greater diameter (more than 24.8 μm).

Biodegradable magnesium-based alloys are very promising materials for temporary implants. However, the clinical use of magnesium-based alloys is often limited by rapid corrosion and by insufficient mechanical stability. Here we investigated RS66, a magnesium-based alloy with extraordinary physicochemical properties of high tensile strength combined with a high ductility and a homogeneous grain size of ~1 μm which was obtained by rapid solidification processing and reciprocal extrusion. Using a series of in vitro and in vivo experiments, we analyzed the biodegradation behavior and the biocompatibility of this alloy. In vitro, RS66 had no cytotoxic effects in physiological concentrations on the viability and the proliferation of primary human osteoblasts. In vivo, RS66 cylinders were implanted into femur condyles, under the skin and in the muscle of adult rabbits and were monitored for 1, 2, 3, 4 and 8 weeks. After explantation, the RS66 cylinders were first analyzed by microtomography to determine the remaining RS66 alloy and calculate the corrosion rates. Then, the implantation sites were examined histologically for healing processes and foreign body reactions. We found that RS66 was corroded fastest subcutaneously followed by intramuscular and bony implantation of the samples. No clinical harm with transient gas cavities during the first 6 weeks in subcutaneous and intramuscular implantation sites was observed. No gas cavities were formed around the implantation site in bone. The corrosion rates in the different anatomical locations correlated well with the local blood flow prior to implantation. A normal foreign body reaction occurred in all tissues. Interestingly, no enhanced bone formation could be observed around the corroding samples in the condyles. These data show that RS66 is biocompatible, and due to its interesting physicochemical properties, this magnesium alloy is a promising material for biodegradable implants.

In course of a study of high strength, ductile alloys based on the Mg–Li system, we have identified a new quaternary phase with a composition of Mg31Zn26Ca13Li8. The structure of this phase was investigated by Transmission Electron Microscopy (TEM) using the Convergent Beam Electron Diffraction (CBED) technique. Full atomic model is proposed using direct methods applied to powder X-ray diffraction data. The phase has a cubic primitive unit cell with lattice parameter a = 9.386(8)A and its crystal symmetry belongs to the P m 3 ¯ (No. 200) space group. The unit cell of the new phase exhibits a new structure type, which is a variant of the Mg2Zn11 structure. The reliability factors characterizing the Rietveld refinement procedure are: Rp = 8.6%, Rwp = 12.4%, RB = 6.9% and Rf = 4.4%.

A strong and ductile Mg–6.0%Zn–1.0%Y–0.6%Ce–0.6%Zr alloy was developed. The alloy was first cast into billets which were rapidly solidified into ribbons, comminuted and extruded. Some of the extrusions were subjected to reciprocal extrusion processing. The microstructures of the alloy prepared by the different processes were analyzed by optical microscopy (OM) as well as high resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM). The microstructure of the cast consisted of coarse grains with average grain size of about 45 μm with intermetallic networks at grain boundaries. The microstructure of the extrusions made of rapidly solidified chips was not uniform; it was fine at the circumference, but coarser in the central area. A low density of defects in the form of unwelded rapidly solidified (RS) ribbon particles in the center of the extrusion was also present. The microstructure of the alloy subjected to reciprocating extrusion was more uniform with average grain size of 1.3 μm and homogeneously dispersed strengthening particles 80 nm in diameter.

Chemical vapor deposition (CVD) of diamond films and wafers is a well established and flexible technology in which deposition parameters control the deposition rate as well as diamond properties, quality and shape. This article deals with surface morphology and crystallography of wafers, with emphasis on twin blocks and twin quintuples. In the study described here we have determined surface facet crystallography of two diamond wafers groups, one that contains Σ3 twin blocks and the other that has a large population of twin quintuplets. The tool used for the study is a scanning electron microscope (SEM) and the technique to identify surface crystallography involves only accurate tilting and surface observation. A basic knowledge of the twin structure enables accurate determination of surface crystallography.

Based on the commercial alloy ZK60 which contains 6%Zn, high strength Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr magnesium alloy bars of 10 to 50 mm in diameters were prepared by rapid solidification (RS) and extrusion processes （RSE）. For those RSE solid bars, the ultimate tensile strengths steadily maintain on a level of 490 to 520 MPa, the elongations are between 6 to 10%. The HV50 hardness is between 85 and 90. In order to reveal materials microstructures both RS ribbons and RSE solid bars, the Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr alloy was analyzed with an optical microscopy (OM), a scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) and an X-ray diffraction apparatus. It was found that the microstructure of the RS ribbon consists of super saturated (Mg) solid solution; thermally stable Mg3Y2Zn3 (W) and Mg7Ce2 intermetallic compound particles which uniformly dispersed interior grains and W and Mg7Ce2 compound networks at grain boundaries. After extrusion, the microstructure of RSE Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6%Zr solid bar consists of the same phases as the RS ribbons. The networks existing at RS ribbon’s grain boundaries were break up into submicron particles and dispersed uniformly on the matrix formed after extrusion.

I am glad to learn that a focus issue, Complex Metallic Phases, will be published in Science and Technology of Advanced Materials (STAM). The articles in this special issue contain original and review papers on fundamentals and applications contributed by experts in the field. The topics cover various approaches to practical applications including catalysts, photonics, high specific strength materials, thermal storage materials and thermal rectification for quasicrystals, as well as related complex compounds. It is exciting to see the great potential of these complex phases, and I look forward to seeing their industrial applications in the foreseeable future. [Formula: see text] Professor Dan Shechtman Recepient of the Nobel Prize in Chemistry 2011 for his discovery of 'quasi-crystals' in 1984.

Corrosion behavior of as-cast and heat treated Mg-Zn-Zr-Y alloy was studied in 1 g/l NaCl solution. The as-cast alloy was the least resistant to pitting corrosion. Its Mg-Zn solid solution matrix was the structural constituent responsible for corrosion susceptibility due to the presence of Zn-lean regions. Homogenization of the Zn distribution within the matrix significantly increased the corrosion resistance of the alloy. Grain boundaries, which contain intermetallic phases, were resistant to corrosion attack, thus impeding corrosion propagation.

We conducted tensile tests of free standing Al/Ti multilayer thin films in order to determine the dependence of yield stress on layer thickness. The multilayers studied were composed of fcc and hcp Ti layers. The Al layers were approximately twice the thickness of the Ti layers. Because a controversy exists concerning the crystalline structure of Ti in Al/Ti multilayers, we also present microstructural results.

Yield stresses, ultimate tensile strengths, and specific strengths of aluminum/titanium multilayer thin films are determined from the results of uniaxial tensile tests. The plasticity in the stress-strain curves, the nature of the fracture surfaces, and the relationship of the yield stress and the bilayer thickness are discussed. Properties are compared with those of other multilayer materials published in the literature.

The presence of face centered cubic Ti and Zr in Zr/Ti multilayers in specimens prepared for transmission electron microscopy is noted. X-ray diffraction shows that in the as-deposited state the multilayers contain the equilibrium hcp Ti and Zr phases, implying that a transformation occurs during thinning of specimens for TEM study.

The equilibrium phases of titanium are hcp under 1155 K and bcc above this temperature. However, titanium has been shown to exist as fcc when its dimensions are small. We have studied the hcp to fcc transformation in thin titanium layers in an effort to characterize the fee titanium and to understand the driving force behind the transformation. Multilayers of titanium and silver were deposited by electron beam evaporation, and examined by X-ray diffraction and by transmission electron microscopy. The lattice parameter of the fcc titanium was measured to be 0.434 nm and the results eliminated lattice mismatch as a driving force, since it has increased by the transformation.

Electrodeposited Cu/Ni multilayers with different modulation lengths Λ = 4–18 nm were examined by means of x-ray diffraction and transmission electron microscopy. Preferred orientations of [111], [110], and [001]-types, as determined from relative x-ray diffraction peak intensities, were seen in the multilayers. By means of computer simulations of the measured x-ray diffraction spectra, several parameters of the multilayers, such as Λ-values and fluctuations ΔΛ, as well as lattice strain, were determined. Multilayers having large Λ were found to be fully relaxed due to interfacial dislocation formation. In short Λ [001]-texture multilayers partial strain relaxation occurs, probably due to the incorporation of Cu into the Ni layers. Both of the processes lead to the diffuse Cu/Ni interfaces. Short wavelength multilayers with a [111]-preferred orientation were almost fully strained. The importance of the [111]-texture in the improvement of mechanical strength of Cu/Ni multilayers resulting from its enhanced ability for stain accommodation is discussed.

The Ti layers in Al/Ti multilayers are shown to transform from hexagonal close packed in the as-deposited multilayers to face centered cubic on ion milling in cross-section. By examining the change in free energy of the system on transformation it is demonstrated that interfacial, surface and strain free energies cannot overcome the theoretically predicted 0.08 eV/atom difference in bulk free energy between f.c.c. and h.c.p. Ti. Based on experimental observations of f.c.c. Ti in multilayers, it is argued that this value is too large.

Titanium layers 40, 90 and 220 nm thick in nickel-titanium multilayer thin films are shown to deposit with a hexagonal close packed structure that transforms to a face centered cubic structure when thinned, using an ion beam, for transmission electron microscopy. Implications for recent reports of polymorphic fcc Ti in multilayers are noted.

A technique for alloy sample preparation, based on thin film deposition, has been developed for a study of binary and ternary compositions. Thin elemental wedge-shaped layers of the components were gradually sputtered in an alternating manner to form multilayered structure. The samples obtained had compositions which depended upon their location on the substrate. Such samples, containing differently composed AuAgCu alloys were heat treated to promote formation of stable phases. The alloys thus formed were studied by X-ray diffraction and various microscopic techniques. This article demonstrates the advantages of this method over conventional bulk-based methods.

Growth features of chemical vapor deposited diamond wafers were studied and their crystallography determined. σ = 3 twins play an important role in the fast growth of diamond wafer as they enable the formation of re-entrant corners along their intersection line with the growing surface. These re-entrant corners serve as preferred nucleation sites for new planes. The facet planes at the surface were found to be either {111} or {001} and the various morphology combinations are discussed in this article.

The twin structure of diamond films grown by plasma-assisted chemical vapor deposition (CVD) was studied by high-resolution transmission electron microscopy. The structure of high-order twins of the type Σ = 9, Σ = 27 and Σ = 81 was investigated and the way they form analyzed. In particular, two types of Σ = 81 were found. The first results from an interaction between four Σ = 3 twin boundaries and the second from an interaction of Σ = 3 with higher-order boundaries, such as Σ = 27. We suggest that a higher-order twin of the type Σ = 243 can form in rare cases. However, such a boundary was not observed in our study.

Thin films of alternating Au, Ag, and Cu wedge‐shaped metal layers were made by magnetron sputtering in order to develop a method for investigation of a multicomponent systems. X‐ray‐diffraction patterns of all as‐deposited samples revealed satellites in the vicinity of (111) reflections, evidence of composition‐modulated artificial superlattice formation. The experimental spectra are well explained by the kinematical diffraction theory for imperfect superlattices. Computer simulations have demonstrated extremely high sensitivity to the fluctuations ΔH/H of the superlattice period H. As a result, a rapid and simple method of ΔH/H determination is proposed.

Growth defects in diamond films grown by plasma-assisted chemical vapor deposition (CVD) were studied by high resolution electron microscopy. Several features of the microstructure were resolved and their importance to the growth of the diamond film was evaluated. The observations included various twin boundaries of the type ∑ = 3, as well as ∑ = 9, ∑ = 27, and ∑ = 81, which form by an interaction of lower order twins. These higher order boundaries are loci of intersection points of growing planes on two adjacent twins and can serve as an indicator for the local crystal growth direction. The central nucleation site for the growing planes in many cases can be traced back to a quintuplet twin point. A twin quintuplet has five re-entrant angles and thus serves as a preferred nucleation site for new planes as the crystal grows.

Rapidly solidified alloys of Au-2wt%Ti, Au-3 wt% Ti and Au-5wt% Ti have been examined using transmission electron microscopy in order to investigate both the nature of structural order induced by rapid solidification and the evolution of long-range order during post-solidification heat-treatment. 〈1½0〉 special-point order is identified as a feature of the as-solidified microstructures and an intermediate state of order, incorporating both elements of the long-range-ordered (D1a) structure and elements of 〈1½0〉 special-point order, is observed to be stable up to the nucleation temperature of the equilibrium (D1a) Au4Ti phase in Au-3 wt% Ti. The evidence from electron diffraction patterns is discussed and interpreted by considering the nature and distribution of the three-dimensional diffuse streaking observed in zone-axis patterns from a variety of different orientations. The compositions examined demonstrate that these materials are members of the ‘special-point’ family of alloys and that incorpo...

Thin alternating layers of Al-Cr were produced by sputtering. Heat treatment transforms them to the icosahedral phase. The effect of the layer thickness on their ability to transform to single-phase icosahedral film was examined and it was found that very thin alternating layers react completely to form a single icosahedral phase, while heat treatment of thicker layers always produced the icosahedral phase with residual aluminium. An attempt has been made to explain the results based on the crystallographic structure of the icosahedral phase.

Bacterial infections are a costly sequela in any wound. The corrosion properties of 0.15, 0.30, 0.45 and 0.60 g of Mg metal were determined in Mueller–Hinton broth by serially measuring the Mg2+ concentrations and pH over 72 h. In addition, the effect of Mg metal, increased Mg2+ concentration and alkaline pH on the in vitro growth of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus were evaluated in three separate experiments. The primary outcome measure for culture studies was colony-forming units/ml compared to appropriate positive and/or negative controls. Regardless of the mass of Mg added, there was a predictable increase in pH and Mg2+ concentration. The addition of Mg and an increase of pH resulted in antibacterial effects similar to the fluoroquinolone antibiotic; however, a simple increase in Mg2+ concentration alone had no effect. The results demonstrate an antibacterial effect of Mg on three common aerobic bacterial organisms, the mechanism of which appears to be an alkaline pH.

Precipitation at 450 °C was studied in melt-spun ribbons containing up to 15 wt pct Mn in solid solution in Al. The as-spun ribbons were microsegregation-free at compositions up to 5 wt pct Mn, but in more concentrated alloys a cellular microstructure was present. Upon annealing, four precipitate phases are observed, some of them being found preferentially on cell boundaries and others being found within the cells. Al6Mn, G, and the Gℍ phase can coexist for long times at 450 °C, but the G phase appears to be slightly more stable. A less stable T phase was detected in Al-5 wt pct Mn foils following short annealing periods. The supersaturation of the Al matrix can persist for many hours in alloys containing up to 3 wt pct Mn, but is essentially gone after 1 hour in alloys with 5 wt pct Mn or more.

Two Al−Cr compounds, known in the literature as the η and e phases, were studied by precession camera single crystal X-ray diffraction and transmission electron microscopy (TEM). The results are different from those reported in the literature. The e Al4Cr phase was found to be hexagonal P63/mmc with lattice parametersa=2.01 nm andc=2.48 nm, and we suggest that it is isomorphous to the Al4Mn μ phase. The η Al11Cr2 phase has a monoclinic (pseudo-orthorhombic) C-centered Bravais lattice witha3≃1.76 nm,b3≃3.05 nm,c3≃1.76 nm, and β≃90 deg and a possible C2/c space group. Single crystals of the η phase are usually twinned.

The mass loss during sliding wear of several quasicrystalline (QC) coatings has been measured. QC coatings of the Al–Cu–Fe, Al–Cu–Fe–Cr and Al–Pd–Mn systems have been investigated and compared with a hardened tool steel and a WC–6% Co hardmetal. The wear rates of the coatings are in general comparable to conventional metallic materials. There is some variation in sliding wear behaviour of different QC coatings.

A Ti-32wt% Fe alloy was rapidly solidified by the melt-spinning technique. Three microstructures are found in the melt-spun ribbon of the alloy: the first contains small FeTi particles in aΒ matrix, the second is a cellular microstructure composed ofΒ and FeTi and the third is a eutectic of these phases. The correlation between various solidification and cooling rates across the ribbon width to the three microstructures is explained.

The mid 1980s benefited from three major scientific announcements that altered our world view on the structure of matter and its properties. These were the discovery of quasiperiodic crystals (QCs), which are commonly referred to as quasicrystals (1984), fullerenes (1985), and high-temperature superconductivity (1986). The discovery of QC was announced to a community active in the mature science of crystallography. Crystallographers, and other scientists who studied the structure of matter and its defects, relied on a series of laws and paradigms undisputed since von Laue performed his first x-ray-diffraction experiments in 1912. One leading paradigm stated that the atomic structure of a crystal is ordered and periodic. Explanations of this paradigm, based oncommon sense, could be summarized as, “It is periodic because it is ordered.”Periodicity implies a set of specific rules, among them the allowed rotational symmetries—namely one-, two-, three-, four-, and sixfold. Fivefold rotational symmetry is excluded. Past textbooks specified this, stating that fivefold rotational symmetry is impossible in periodic structures. Other books stated the impossibility of such symmetry in crystals.Paradigms are based on experience rather than on a rigorous, scientific study process. Therefore when proven wrong, they are difficult to uproot. From 1912 to 1984, nothing shook the paradigm, “Order in crystals is periodicity.” Incommensurate structures challenged the paradigm for a while but were soon found to be a modulation of periodic crystals, saving the paradigm. However in the background, a series of articles broadened the scope of crystallography into hyperspace and prepared the mathematical platform from which the science of quasiperiodicity in crystals could take off.

The acoustic field inside a surface acoustic wave device was studied by means of double‐crystal x‐ray diffraction. Angular satellites in the diffraction pattern were observed due to the coherent scattering on the acoustic superlattice. Satellite dynamics allows determination of the acoustic wave amplitude. Due to the sensitivity of x‐ray diffraction to the direction of atomic displacements, the amplitude of different polarization components in the Rayleigh wave can be obtained.

Features in lattice image micrographs of chemical vapor deposited diamond can be interpreted as Moire fringes that occur when viewing twin boundaries that are inclined to the electron beam. The periodicities in images of inclined twin boundaries with Σ=3 and Σ=9 misorientations have been modeled by computer graphic simulation.

Crystallography has been one of the mature sciences. Over the years, the modern science of crystallography that started by experimenting with x-ray diffraction from crystals in 1912, has developed a major paradigm – that all crystals are ordered and periodic. Indeed, this was the basis for the definition of "crystal" in textbooks of crystallography and x-ray diffraction. Based upon a vast number of experimental data, constantly improving research tools, and deepening theoretical understanding of the structure of crystalline materials no revolution was anticipated in our understanding the atomic order of solids. However, such revolution did happen with the discovery of the Icosahedral phase, the first quasi-periodic crystal (QC) in 1982, and its announcement in 1984 [1, 2]. QCs are ordered materials, but their atomic order is quasiperiodic rather than periodic, enabling formation of crystal symmetries, such as icosahedral symmetry, which cannot exist in periodic materials. The discovery created deep cracks in this paradigm, but the acceptance by the crystallographers' community of the new class of ordered crystals did not happen in one day. In fact it took almost a decade for QC order to be accepted by most crystallographers. The official stamp of approval came in a form of a new definition of "Crystal" by the International Union of Crystallographers. The paradigm that all crystals are periodic has thus been changed. It is clear now that although most crystals are ordered and periodic, a good number of them are ordered and quasi-periodic. While believers and nonbelievers were debating, a large volume of experimental and theoretical studies was published, a result of a relentless effort of many groups around the world. Quasi-periodic materials have developed into an exciting interdisciplinary science. This talk will outline the discovery of QCs and describe the important role of electron microscopy as an enabling discovery tool.

Quasicrystals (QCs) are known to exhibit unique properties as a result of their unique quasiperiodic structure. Real quasicrystalline (QC) materials, however, may exhibit complex phase structures, and as a consequence, their properties may differ from expectations. In the present work, QC coatings of the Al–Cu–Fe, Al–Cu–Fe–Cr, and Al–Pd–Mn systems were prepared by a plasma spray process, followed by heat treatments in the range 500–800 °C. The phase structure and evolution of the coatings were evaluated, and thermal diffusivity, hardness, and friction coefficient were measured. The presence of quasicrystalline and crystalline phases and their influence on these properties is systematically considered for the first time. Broadly, the coatings exhibit the properties expected of QC materials, low thermal diffusivity, high hardness, and low coefficients of friction, but it is also shown that these properties can be sensitive to the phase structure of the coatings. This suggests that phase structure may be manipulated by heat treatment to optimize the properties of QC coatings.

The influence of grain orientation on the friction and wear behavior of single-phase quasicrystalline alloys is investigated. Pin-on-disc wear tests and friction coefficient measurements have been performed on bulk samples of icosahedral phase AlPdMn and decagonal phase AlNiCo alloys. Wear behavior has been evaluated by optical microscopy, scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). Coefficient of friction values of the decagonal AlNiCo alloy are found to be widely scattered (between 0.03 and 0.55) compared to the far more consistent values of the icosahedral alloys. This is explained by considering the significant variation in wear behavior that is observed between different – sometimes adjacent – oriented grains in the decagonal specimens.

The effects of nitriding and carburizing chromium substrates on the nucleation of CVD diamond were studied. Surface morphology, incubation time and diamond particle density at the initial stages of deposition were examined using high resolution scanning electron microscopy (HRSEM) as a function of the substrate pretreatment. The presence of amorphous carbon, as well as residual stress in the deposited films were determined by Raman spectroscopy.